1990 volvo 740 problem

[somiprika]

This is my problem. My problem first starting during the summer. It was very hot outside, and in the morning i take my car to work with no problem. When i get off of work around 3pm, it was about 90 degrees, my volvo would not start. I would come back to work around 9pm when it was cool outside, and it would start no problem. We found when it is that hot outside it does not recieve power to the fuel pump. We rigged a switch from the battery to the fuel pump and when it is hot outside, and i turn the switch on, the volvo starts. I was using the switch all summer. About 3 weeks ago, i went to the grocery store and when i came out, the car would not start at all. We found out that it had good sparks and fuel pressure but still it would not start. Now three weeks later the car starts but it only starts on the switch. it will not start without it. A couple people suggested it is the computer. We checked air flow sensor, they think that is not the problem. We also checked the injectors, they are also good. If it is the computer, do we need the same serial (id) number or can we use a different one?

[Kmaniac in California USA]

It sounds to me like your fuel pump relay has gone bad. The relay is located behind the fuse box, which is behind the ashtray in the center console. The fact that it didn's start once with the bypass switch turned on leads me to think that your fuel pumps are going bad due to dirt contamination. Oh, in case you didn't know it, your car has two fuel pumps. Check your in-tank fuel pump fuse to see if it is blown. If so, you need to replace both fuel pumps and the filter sock in the tank. I suggest you pull the in-tank fuel pump, which is mounted on the fuel pick up and inspect the filter sock on the pick-up end of the pump. Should you have any deterioration or holes in the sock, both of your pumps should be replaced. I will attach my story to this post for your information. Happy trouble-shooting.

September 3, 2004

I, too, have a 1986 740 GLE sedan with B230F (no turbo, fuel injection) and automatic transmission. It always starts and runs well when cold, but will randomly fail to start when hot. I have owned the car for two weeks (no wonder I got such a great deal on this) and this has occurred at least six times. A couple of times it restarted after 5 minutes, but once it sat for six hours until the sun went down before starting again. Sometimes when it has its fit, it sounds like is tries to fire, but then just cranks. I am waiting for the next incident to confirm whether it is lack of spark or fuel. Will keep you posted. In the last 4000 miles the car got new spark plugs, wires, cap, rotor and coil, as well as a new in-tank fuel pump and filter sock. The fuel pump relay behind the ashtray works and clicks every time. Any suggestions from others who have experienced the same problem would be appreciated.

September 4, 2004

Well, my Volvo did it again today. At 7:00 AM and 65 F temperature, it started and drove fine as I got my morning coffee. Six hours later, after sitting in the hot California sun on this 90 F day, it failed to start in my driveway. I hooked up my inductive pick-up timing light to the ignition system and got plenty of spark on all four cylinders and the coil. Leads me to think the problem is hiding in the fuel injection system. The car has 203,200 miles on the odometer and everything associated with the fuel injection looks original, except for the fuel filter. Any ideas which parts of the fuel injection system would be affected by the heat of the sun on a hot day?!? At least I know it is not the ignition system. I will keep all posted as I progress through the fuel system.

September 6, 2004

Eureka!! I think I solved the Problem!!!

I drove my Volvo on errands this morning, ending up at the local auto parts store to purchase fuel injection pressure testing equipment. When I went to leave, it wouldn't start. It was a warm California day with the temperatures reaching into the 90's F. I sat with car for two hours trying repeatedly to start it. It would just crank. My timing light indicated strong spark. I got a ride home and returned with my tools in another vehicle. I spent another hour trying to figure out how to hook up the test equipment. Then a guy from the parts store comes out and says that he thinks it is the fuel pump. He then hands me a rock and tells me to tap on the fuel pump a few times. This should knock loose anything that might be hanging up inside the pump. So I take the rock, crawl under the car, and tapped the fuel pump about a dozen times. I get out, get into the car, turn the key and it starts right up! I immediately purchased a new replacement fuel pump, drove the car home and replaced the fuel pump. I am 99% sure that this will cure the problem. I will check back in a couple weeks to let you know how this is going.

October 1, 2004

After four weeks, the car starts first time, every time. No more starting problem. Both new fuel pumps did the trick!

Looking back, it is clear that the original in-tank pump was not working when I bought the car. I found fuse #11 blown a few days after buying the car. I replaced the in-tank pump for good measure. Since I was going into the tank to look at it, it was easier to replace at the same time than to put the old one back in. I discovered the old filter sock had deteriorated and had at least two holes in the sock. I suspect dirt entered the in-tank pump, fouling it and causing the fuse to blow. I further suspect the main fuel pump was fouled with dirt from the broken filter sock, which caused the intermittent starting.

Should you encounter a bad main fuel pump on your car, always inspect and/or replace the in-tank fuel pump, so that you can verify the condition of the filter sock. A bad or deteriorated in-tank filter sock will lead to fouling both fuel pumps with dirt. (Should you go to the trouble of taking out the in-tank pump, you may as well replace it while you got it out.)

November 17, 2004 (Response to a similar complaint)

Reading your story was like de ja vu. I had a similar problem with my 1986 740 GLE, which is documented in the "1986 740 GLE inconsistent starting" post. You can read my experiences there.

I need to point out that your car has two fuel pumps, which work in series. There is a small pump in the gas tank, known as the "in-tank" pump. The other is the main fuel pump, which is mounted together with the fuel filter, in a cradle, bolted to the underside of the car, under the driver's seat. Both pumps receive electric power through the same fuel pump relay, which is found behind the ashtray in the console. Though powered through the same relay, each pump circuit is protected by separate fuses. Also, although both pumps work in series, the operation of both pumps are not required for the car to run. The car will operate normally using the main fuel pump only. However, it will not run with just the in-tank pump only.

If you haven't done so already, check the fuse for the in-tank fuel pump. It is fuse number 11 in my 1986 740. Three days after buying my Volvo last August, I found the in-tank pump fuse blown. No telling how long this had been this way. Out of general principle, I pulled out the in-tank pump. I found the fuel pick up filter sock deteriorated with at least two holes in the sock. I suspect the deteriorated sock allowed debris to enter the pump and jam it, resulting in the blown fuse. Since I had the in-tank pump out, I replaced it and the filter sock.

My suggestion for you is to find and carry with you a rock, which is big enough to fit in your hand. The next time your car refuses to start, reach under your driver door, locate the main fuel pump, and strike the pump a few times with the rock. Then try to restart the car. If it starts right away, then your main fuel pump is the problem and should be replaced.

Please note, too, the main fuel filter is placed down stream of the main fuel pump. If the in-tank filter sock has deteriorated, unfiltered fuel will enter both the in-tank and main fuel pumps before seeing another filter. If you find that the main fuel pump needs replacement, it makes good sense to pull the in-tank pump and inspect the condition of the filter sock. And if you go to the trouble of pulling this pump, you may as well replace it and the filter sock for good measure. A new main fuel pump can be quickly destroyed by unfiltered fuel, if the in-tank fuel filter sock has deteriorated and is not replaced at the time of main fuel pump replacement.

The in-tank pump and filter sock cost me $50. The main fuel pump cost me $125. I put both in myself. Each pump took me about 4 hours of time each to replace, since this was the first time for me for each part. If you do this yourself, disconnect the fuel lines from the tank before removing the main fuel pump, to prevent the fuel from siphoning out of the tank. Work in a well ventilated area, free of ignition sources.